The overall aim of this project is to map the. The neural basis of gesture processing has received a great deal of attention in the last several years, particularly in connection with the mirror neuron theory of action understanding. This theory states that gestures are understood via motor simulation in the observer. Sign language provides a unique perspective on this issue given its extremely rich gestural system, its easy accessibility (as opposed to speech gestures which are largely obscured from view), and the opportunity to compare linguistic and non-linguistic forms of gestural processing. Sign language bridges the gap between the visuo-manual studies in animal models where mirror neurons were discovered and human language, where there is a tremendous concentration of research on the mirror system. There is substantial clinical importance as well, as the mirror system has been implicated in a range of acquired and developmental disorders ranging from apraxia and aphasia to autism. If therapies are being developed based on a motor simulation model of understanding, it is critical to have information regarding the validity of these claims. Sign language provides an ideal testing ground. In terms of theory, a dorsal-ventral model of gestural processing guides our investigations. Thus, the proposed project builds on a decades-long program of investigation into the neural basis of sign language and has four specific aims. Aim 1: Map of basic language functions in deaf signers using large-scale lesion-deficit mapping. Aim 2: Map the relation between perception and production of meaningless gestures using lesion and fMRI approaches. Aim 3: Map the relation between recognition and production of meaningful action and object-related gestures using lesion and fMRI approaches. Aim 4: Map the relation between recognition and production of pantomime vs. signed gestures using lesion and fMRI approaches. PUBLIC HEALTH RELEVANCE: Communicative gestures, both linguistic and nonlinguistic, pervade human social interaction Disorders affecting the ability to generate or understand communicative gestures in the form of aphasias, apraxias, or syndromes affecting social perception, can have devastating personal and social consequences. For this reason, it is a priority to understand the neural basis of gestural communication and how these forms interact at the neural level.